The UKCISA website now contains separate pages dealing with free hospital treatment in:
You can read about who is entitled to free hospital treatment from the NHS
in each of those places, for courses of treatment that start on or after
6 April 2015. The information is likely to change over time, as the
devolved administrations release more information.
There is a separate page explaining who was entitled to free NHS hospital treatment across the UK, for courses of treatment that started before 6 April 2015.